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This paper investigates thermal mixing caused by the inflow from one or two round, horizontal, buoyant jets in a water storage tank, which is part of a thermal solar installation. A set of experiments was carried out in a rectangular tank with a capacity of 0.3 m3, with one or two constant temperature inflows. As a result, two correlations based on temperature measurements have been developed. One of the correlations predicts the size of a zone of homogenous temperature, referred to herein as the mixing zone, which develops when a single hot inflow impinges on the opposite wall of the tank. The other identifies the degree of mixing resulting from the interaction between a hot inflow and a cold inflow located below the hot one. The correlations are combined with energy balances to predict the amount of hot water available in a tank with open side inlets and the corresponding temperatures of the outflows. Outdoor measurements were also performed in a solar installation, in which a commercial water storage tank with a 1.5 m3 capacity, heated by a solar collector array with a useful surface area of 42.2 m2, drives a LiBr–H2O absorption chiller. Comparison of the predicted and measured outflow temperatures under a variety of weather conditions shows a maximum difference of 3 °C.

The devolatilisation step of coal is a vital stage in both air–coal and oxy-coal combustion and there is interest in whether methods of estimating the reaction parameters are similar for both cases. A network pyrolysis model, the FG-DVC (Functional Group-Depolymerisation Vaporisation Cross-linking) code was employed to evaluate the effect of temperature (1273–1773 K) and heating rate (104–106 K/s) on the devolatilisation parameters of two coals of different rank. The products distribution between char and volatiles, and volatiles and NH3/HCN release kinetics were also determined. In order to assess the accuracy of the FG-DVC predictions, the values for nitrogen distribution and devolatilisation kinetics obtained for a temperature of 1273 K and a heating rate of 105 K/s were included as inputs in a Computational Fluid Dynamics (CFD) model for oxy-coal combustion in an entrained flow reactor (EFR). CFD simulations with the programme default devolatilisation kinetics were performed. The oxygen content in oxy-firing conditions ranged between 21% and 35%, and air-firing conditions were also employed as a reference. The experimental coals burnouts and oxygen concentrations from the EFR experiments were employed to test the accuracy of the CFD model. The temperature profiles, burning rates, char burnout and NO emissions during coal combustion in both air and O2/CO2 atmospheres were predicted. The predictions obtained when using the CFD model with FG-DVC coal devolatilisation kinetics were much closer to the experimental values than the predictions obtained with the ANSYS Fluent (version 12) program default kinetics. The predicted NO emissions under oxy-firing conditions were in good agreement with the experimental values. The present study was carried out with financial support from the Spanish MICINN (Project PS-120000-2005-2) co-financed by the European Regional Development Fund. L.A. and J.R. acknowledge funding from the CSIC JAE program, which was cofinanced by the European Social Fund, and the Asturias Regional Government (PCTI program), respectively. MG acknowledges financial support from E.ON UK, and for an EPSRC Dorothy Hodgkin Postgraduate Award. We also thank Dr L Ma for helpful discussions. Peer reviewed

Fossil fuel based power generation is and will still be the back bone of our world economy, albeit such form of power generation significantly contributes to global CO2 emissions. Solar energy is a clean, environmental friendly energy source for power generation, however solar photovoltaic electricity generation is not practical for large commercial scales due to its cost and high-tech nature. Solar thermal is another way to use solar energy to generate power. Many attempts to establish solar (solo) thermal power stations have been practiced all over the world. Although there are some advantages in solo solar thermal power systems, the efficiencies and costs of these systems are not so attractive. Alternately by modifying, if possible, the existing coal-fired power stations to generate green sustainable power, a much more efficient means of power generation can be reached. This paper presents the concept of solar aided power generation in conventional coal-fired power stations, i.e., integrating solar (thermal) energy into conventional fossil fuelled power generation cycles (termed as solar aided thermal power). The solar aided power generation (SAPG) concept has technically been derived to use the strong points of the two technologies (traditional regenerative Rankine cycle with relatively higher efficiency and solar heating at relatively low temperature range). The SAPG does not only contribute to increase the efficiencies of the conventional power station and reduce its emission of the greenhouse gases, but also provides a better way to use solar heat to generate the power. This paper presents the advantages of the SAPG at conceptual level.

Thin-film photovoltaics (PV) cells offer several benefits over conventional first-generation PV technologies, including lighter weight, flexibility, and lower power generation cost. Among the competing thin-film technologies, chalcogenide solar cells offer promising performance on efficiency and technological maturity level. However, in order to appraise the performance of the technology thoroughly, issues such as raw materials scarcity, toxicity, and environmental impacts need to be investigated in detail. This paper therefore, for the first time, presents a cradle to gate life cycle assessment for four different emerging chalcogenide PV cells, and compares their results with copper zinc tin sulfide (CZTS) and the commercially available CIGS to examine their effectiveness in reducing the environmental impacts associated with PV technologies. To allow for a full range of indicators, life cycle assessment methods CML 2001, IMPACT 2002+, and ILCD 2011 were used to analyse the results. The results identify environmental hotspots associated with different materials and components and demonstrate that using current efficiencies, the environmental impact of copper indium gallium selenide (CIGS) for generating 1kWh electricity was lower than that of the other studied cells. However, at comparable efficiencies the antimony-based cells offered the lowest environmental impacts in all impact categories. The effect of materials used was also found to be lower than the impact of electricity consumed throughout the manufacturing process, with the absorber layer contributing the most to the majority of the impact categories examined. In terms of chemicals consumed, cadmium acetate contributed significantly to the majority of the environmental impacts. Stainless steel in the substrate/insulating layer and molybdenum in the back contact both contributed considerably to the toxicity and ozone depletion impact categories. This paper demonstrates considerable environmental benefits associated with non-toxic chalcogenide PV cells suggesting that the current environmental concerns can be addressed effectively using alternative materials and manufacturing techniques if current efficiencies are improved. Peer Reviewed

The goal of this paper is to assess the suitability of hybrid PVT systems for the provision of electricity and hot water (space heating is not considered) in the UK domestic sector, with particular focus on a typical terraced house in London. A model is developed to estimate the performance of such a system. The model allows various design parameters of the PVT unit to be varied, so that their influence in the overall system performance can be studied. Two key parameters, specifically the covering factor of the solar collector with PV and the collector flow-rate, are considered. The emissions of the PVT system are compared with those incurred by a household that utilises a conventional energy provision arrangement. The results show that for the case of the UK (low solar irradiance and low ambient temperatures) a complete coverage of the solar collector with PV together with a low collector flow-rate are beneficial in allowing the system to achieve a high coverage of the total annual energy (heat and power) demand, while maximising the CO2 emissions savings. It is found that with a completely covered collector and a flow-rate of 20L/h, 51% of the total electricity demand and 36% of the total hot water demand over a year can be covered by a hybrid PVT system. The electricity demand coverage value is slightly higher than the PV-only system equivalent (49%). In addition, our emissions assessment indicates that a PVT system can save up to 16.0tonnes of CO2 over a lifetime of 20years, which is significantly (36%) higher than the 11.8tonnes of CO2 saved with a PV-only system. All investigated PVT configurations outperformed the PV-only system in terms of emissions. Therefore, it is concluded that hybrid PVT systems offer a notably improved proposition over PV-only systems. © 2014 The Authors.

©2020 Elsevier Ltd. All rights reserved. This document is the Published version of a Published Work that appeared in final form in Applied Energy. To access the final edited and published work see https://doi.org/10.1016/j.apenergy.2020.114753 The demand for biodiesel as an alternative and potentially renewable fuel is constantly rising. Biodiesel production from lipids in supercritical conditions offers several advantages over other catalytic processes. These advantages include high-efficiency production, environmental friendliness and the possibility of using a broad range of feedstock sources. As a consequence, there is a great interest in biodiesel production research using supercritical fluids as a sustainable technology option. In this sense, bibliometric reviews can be very useful for the interpretation of scientific production and research trends in this field. Thus, this work presents a scientometric study on biodiesel production research under supercritical conditions from 2001 to 2019, based on the Web of Science© database. 608 articles were analyzed and the parameters considered were: (i) publication type, language and output characteristics, (ii) Lotka's Law, Price's index and h-index, (iii) authors, countries and institutions collaboration analysis, (iv) publication performance by authors, journals, institutions and countries and (v) author keywords, single title words and keywords Plus analysis. The productivity patterns of authors, journals, institutions and authors keywords were found to fit Lotka's law. In terms of feedstock used in supercritical conditions, the bibliometric analysis showed a clear transition from first- to third-generation biodiesel, with special attention paid to the experimental study of supercritical reaction conditions. By contrast, further process optimization, the reduction of the severity of the supercritical conditions through devised strategies to lower energy consumption and further economic analysis are still needed, among other factors, for the real implementation of the technology.

Abstract The need to reduce both energy consumption and greenhouse gas emissions has boosted the interest in using thermoelectric generators (TEGs) as waste heat energy harvesters. High-power TEGs are usually formed by an array of commercial thermoelectric modules (TEMs). Recent studies have analyzed the effects of using different types of electrical connections between TEMs in TEGs to produce electric power, but the effects of using different thermal configurations between TEMs have not been fully examined. Here, both electrical and thermal effects have been investigated using a numerical model developed with GT-SUITE software, which has been validated with laboratory data. TEGs with a number of TEMs between 1 and 100 distributed in different patterns along the exhaust pipe have been simulated under three engine regimes. For a given TEM geometrical pattern and engine regime, results prove the existence of an optimum number of TEMs, beyond which the total extracted power decreases. A mixed spatial distribution of TEMs generates more power than either the pure series or the pure parallel topologies. Finally, a methodology is proposed to choose an appropriate pattern of TEMs for a TEG installed in a system with variable regimes. This method is applied to a mid-size automotive diesel engine.